#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int sum(int n) {
    if (n > 1)
        return n + sum(n - 1);
    else
        return 1;
}
int main() {
    int n = 0;
    scanf("%d", &n);
    printf("%d", sum(n));
    return 0;
}